In the new study, scientists investigated another similar beast
— extinct carnivores known as
mosasaurs, generally thought of as gigantic finned marine
lizards similar and perhaps even related to present-day monitor
lizards.

The mosasaur fossils were unearthed starting in 1999 from an
open-pit mine in the Bakony Hills of western Hungary.

The researchers discovered several 84-million-year-old specimens,
ranging from small juveniles to adults 20 feet (6 meters) long
that had limbs like a land-dwelling lizard, a flattened,
crocodile-like skull, and a tail unlike other known members of
the mosasaur family.

The fossils were discovered in areas that were once freshwater
floodplains home to fishes, amphibians, turtles, crocodiles,
terrestrial lizards, pterosaurs, dinosaurs and birds. This
newfound reptile appears to be the first known freshwater
mosasaur, an animal comparable to modern river dolphins now seen
in the Amazon, Ganges and Yangtze rivers.

The new species is named Pannoniasaurus inexpectatus.
"Pannonia" refers to the part of Hungary it was found in,
"saurus" means lizard, and "inexpectatus" refers to the
unexpected occurrence of this mosasaur in freshwater
environments. [T.
Rex of the Seas: A Mosasaur Gallery]

"The size of Pannoniasaurus makes it the largest known
predator in the waters of this paleo-environment," said
researcher László Makádi, a paleontologist at the Hungarian
Natural History Museum.

The evolutionary history of mosasaurs suggested by these new
findings is remarkably similar to that of whales and dolphins,
Makádi told LiveScience.

"To the best of our knowledge, the ancestors of mosasaurs and of
some related reptiles moved from land to aquatic realms at least
100 million years ago. Whether these were marine or freshwater
environments, it is [uncertain], however some finds in Japan
suggests the latter," Makádi said.

"Then sometime between this event and 85 million years before
present — the age of our locality in Hungary — some primitive
members of the already-marine mosasaurs adapted to freshwater
life. Pannoniasaurus represents these. This scenario is
very similar to the evolutionary history of cetaceans — whales,
dolphins."

The researchers plan to investigate new Pannoniasaurus
fossils as they pop up in the hopes of learning more about the
beast's biology, such as how it moved and what it might have
eaten, Makádi said.